A Doherty power amplifier is a highly efficient power amplifier (PA for short in this application). Generally, a Doherty power amplifier includes a carrier PA (also called a main PA) and a peak PA (also called an auxiliary PA).
As shown in FIG. 1, a typical Doherty power amplifier includes a carrier power transistor (power transistor) and a peak power transistor. An output end of the carrier power transistor and an output end of the peak power transistor are connected to output matching circuits separately. An output end of the output matching circuit connected to the output end of the carrier power transistor is connected to one end of a λ/4 transmission line, and the other end of the λ/4 transmission line, after power synthesis with an output end of the output matching circuit connected to the output end of the peak power transistor, is connected to one end of another λ/4 transmission line, and the other end of the another λ/4 transmission line is connected to a transmission line, such as a 50 ohm cable.
Herein, the carrier power transistor and the peak power transistor may be power transistors of a same model, and may also be power transistors of different power levels. The carrier power transistor and the peak power transistor are generally packages of a power amplification transistor, and each the package includes an active die (die, die for short in this application), a bonding wire, and a flange. The flange is a base of a radio frequency power amplification channel; the active die is used to amplify a radio frequency signal; the bonding wire is used to connect the active die and an input end or an output end of the radio frequency power amplification channel, and the input end or the output end of the radio frequency power amplification channel is an input pin or output pin of the package. The package is connected to a peripheral circuit, such as an output matching circuit, by using the input pin or the output pin.
It can be learned from the foregoing that in a typical Doherty power amplifier, an output matching circuit and an impedance conversion circuit implemented by a λ/4 transmission line are required. However, both an area of the output matching circuit and an area of the λ/4 transmission line are relatively large, and therefore an area of the Doherty power amplifier is relatively large.